1. Field of the Invention
The invention relates to an internal combustion engine with at least one cylinder and at least one gas exchange valve controlled by a first cam on a first camshaft and by a second cam on a second camshaft, with at least one camshaft having an adjustable phase position in order to modify the control times of the gas exchange valve, with the first cam acting upon an actuating means and the second cam acting upon an actuating means which actuates the gas exchange valve, with the actuating means being arranged in such a way that the gas exchange valve opens only when both the first cam and the second cam are acting upon the actuating means. The invention further relates to an apparatus for engaging an additional cam elevation for an internal combustion engine with at least one gas exchange valve that can be actuated via a cam of a camshaft, comprising at least one pressure body which is held in a displaceable manner in a radial transverse bore of the camshaft preferably in the region of the base circle of the cam and which is adjustable by means of an actuating rod which is arranged in a displaceable manner axially within the camshaft between at least two positions, with the actuating rod comprising at least one ramp surface in the contact area of the pressure body, with the path of displacement of the pressure body being delimited in the transverse bore radially to the outside and/or the twistability of the pressure body in the transverse bore being limited. The invention further also relates to an internal combustion engine with a variable valve actuating device with at least a divided cam arrangement which comprises at least one cam fixedly connected to the camshaft and at least one additional cam which is twistable between at least two positions about a rotational axis parallel to the camshaft axis.
2. The Prior Art
It is known that internal combustion engines can be optimized in such a way that the valve control times of the intake and exhaust valves are changed depending on the respective operating state.
Such a measure allows increasing both the engine output as well as reducing fuel consumption and exhaust gas emissions. One known possibility for realizing such a change in the valve control times is to slightly twist the camshaft relative to the normal position, which camshaft performs the actuation of the respective valve. It is obvious that in this manner the duration of the valve opening and the valve lift during the opening cannot be changed.
A method and an apparatus for changing the valve control times are known from EP 0 596 860 A, in which each cam is composed of two semi-cams which can be twisted relative to each other. It is thus possible to change the duration of the valve opening. In order to enable the adjustment of the semi-cams independent from each other, an inside shaft is provided within a hollow drilled camshaft which can be twisted relative to the camshaft. Although it is possible in this way to set the start of the valve opening as well as the end of the valve opening within certain limits independent from each other, the valve lift is still predetermined and the apparatus is in addition complex and costly.
A further solution for realizing valve control times in which the opening and closing movement can be changed independent from each other is described in EP 0 909 882 A. A valve is actuated by two camshafts, of which one substantially initiates the valve opening movement and the other the valve closing movement. It is also disadvantageous in this solution that the valve lift cannot be changed and that the mechanical complexity is high.
An internal combustion engine is known from EP 1 375 843 A of the applicant which comprises a valve actuating mechanism which offers an improvement of the solutions as described above. The valve actuation occurs in a hydraulic manner. This hydraulic actuation is undesirable in some cases when hydraulic requirements are opposed to the same.
DE 24 56 752 shows a purely mechanical solution which offers an only very limited adjusting range however.
Apparatuses for engaging an additional cam elevation are used for exhaust gas recirculation devices, decompression devices and exhaust gas braking devices.
In MTZ February 2003, annual edition 64, page 100, a switchable camshaft for an engine brake is known, comprising an apparatus for engaging an additional cam elevation for an internal combustion engine of the kind mentioned above. The path of displacement and the twistability of the pressure body is delimited by two buckles screwed onto the surface of the camshaft on both sides of the pressure body. The number of the parts is relatively high, mounting is complex and operational reliability over prolonged operating periods is not ensured.
A decompression device with an actuating rod arranged within a camshaft is known from EP 1 247 951 A2, comprising a ramp surface formed by a circumferential groove, through which a pin can be radially displaced in the region of a cam base circle. The actuating rod is actuated by means of a cable pull.
U.S. Pat. No. 1,439,798 discloses a decompression device with an actuating rod arranged in a camshaft, which actuating rod comprises ramp surfaces in the region of a pin arranged radially in the camshaft in the region of a base circle of a cam, which ramp surfaces act upon the pin. By sliding the actuating rod in the direction of the longitudinal axis of the camshaft, the radial pin slides along the ramp surfaces and is displaced in the radial direction. The extension and retraction of the radial pin occurs in a desmodromic manner.
Furthermore, simple valve actuation devices with rigid additional cams are known which ensure an internal recirculation of exhaust gas in a cost-effective and reliable manner. The missing deactivation capability in the case of additional cam elevation is disadvantageous in certain load cases in the exhaust gas cycle.
A variable valve actuation device for an internal combustion engine is known from U.S. Pat. No. 5,136,887 which comprises a cam that can be twisted by means of a control source arranged within the camshaft.
U.S. Pat. No. 4,498,352 shows a camshaft arrangement with a divided cam. The two partial cams can be twisted relative to each other by means of a control shaft arranged within the hollow camshaft. FR 1 109 790 A shows a similar cam arrangement with divided cams.
Camshaft arrangements with divided cams are further known from the publications U.S. Pat. No. 4,522,085 and DE 29 21 645 A1, with the cams being twistable relative to each other by means of a control shaft arranged as a pull rod. In order to ensure this, the control shaft comprises grooves extending in an inclined or screw-like manner on its jacket surface, into which engage projections of the cam parts twistably arranged on the camshaft.
Further camshafts with divided cam arrangement in which two cam parts can be twisted against each other are known from the publications WO 94/19585 and U.S. Pat. No. 4,917,058 A. One of the two cam parts is twisted by an outer twisting device relative to the other cam part.
The known arrangements all have the disadvantage that they require a high number of components of complex constructional configuration, which thus substantially increases the amount of production work.
It is the object of the present invention to provide an internal combustion engine with a valve control which avoids such disadvantages and allows for high degrees of freedom in setting the valve opening times and the height of lift of the valve movement. The advantages of the solution known from EP 1 375 843 A shall be achieved by a purely mechanical solution, with the complexity being as low as possible, so that a cost-effective production and maintenance can be ensured. It is a further object of the invention to provide a cost-effective, sturdy and reliable apparatus for engaging an additional cam elevation in the simplest possible way. It is a further object of the invention to reduce the constructional effort for a variable valve actuating device in an internal combustion engine of the kind mentioned above.